The present invention relates to check valves and, more particularly, to detector check valves for use in fire protection systems.
A typical fire protection system includes a riser or supply pipe connected to a water main. Branches are connected to the riser and extend throughout the building to the areas to be protected. Drop pipes are secured to the branches. Each drop pipe supports an automatic sprinkler head. Each head may include a body defining a nozzle, a deflector, a cap or plug within the nozzle and a thermal trigger. When a predetermined temperature is reached indicating a fire condition, the trigger releases the cap permitting water or other fire suppression fluid to flow from the nozzle to the area of the fire.
Such systems may include a detector check valve in the supply piping to the riser. Generally, the check valve, which permits flow in one direction only, includes a clapper or valve element which is held against a valve seat so that a predetermined pressure differential across the valve is necessary to permit flow through the valve. The valve differential permits the installation of a by-pass water meter which is used by water authorities to detect small flows. In addition, the clapper is biased towards its closed position in a positive fashion.
Many of the check valves heretofore provided have included coil springs which operate in tension to bias the check valve clapper towards its seat. Depending upon the design of such a detector check valve, it is possible to overstress the spring and change its spring rate. The hook ends of the spring define stress risers which may result in failure of the spring after cycling of the valve. Debris in the water may lodge between the coils of an extension spring and prevent the spring from closing the clapper or valve element.
A need exists for an improved detector check valve having increased reliability and improved failure characteristics.